Use of Thermal Conduction Heating for the Remediation of DNAPL in Fractured Bedrock

This paper presents the first full-scale remediation at a fractured rock site using Thermal Conduction Heating (TCH), also known as In-Situ Thermal Desorption (ISTD). A 90-ft deep TCE source area was treated thermally, including thick zones of saprolite and gneiss bedrock. The thermal treatment used 24 heater borings/wells, and operated for 148 days, after which an average temperature of approximately 100 o C was achieved. The ISTD remediation work was highly successful at reducing soil, rock and groundwater concentrations at this confidential facility. Post remediation soil sampling indicated that the 95% UCL of the mean concentration of TCE in soil within the treated area was 17 µg/kg. This was significantly lower than the remedial goal of 60 µg/kg. In addition, groundwater concentrations within the treatment zone were reduced by between 74.5% and 99.7%. The total mass of VOCs removed from the subsurface during the ISTD remediation was approximately 12,000 lbs, almost all of which was TCE.